Fryer

ABSTRACT

A fryer for business use is provided which can prevent degradation of cooking oil, secure a good cooking environment and improve a work efficiency. To this end, the fryer of this invention comprises: a water tank  32, 82  to store water; an oil tank  9, 51  arranged above the water tank to store the cooking oil in contact with the stored water in the water tank; a heater  13, 52  arranged in an oil layer in the oil tank; and an oil delivery pipe  10, 61  through which to draw the cooking oil in the oil layer by a pump  29, 64  and release it onto a bottom of the water tank  32, 82 ; wherein the released cooking oil rises through the water layer and flows into a lower part of the oil layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/576,411, filed Mar. 30, 2007, which is a 371 of PCT/JP05/18562 filedOct. 6, 2005.

TECHNICAL FIELD

The present invention relates to a fryer mainly used for businesspurposes and more particularly to a fryer equipped with a device forautomatically removing deep-fried batter balls and an automatic cookingoil cleaning device to keep the cooking oil clean, prevent itsdegradation and thereby extend its useful life.

BACKGROUND ART

Conventional fryers store a specified amount of cooking oil in an oiltank and heat it with a gas or electric heater. With the cooking oilheated to a set temperature, the fryer stands by and food materials arethrown in for frying. After a predetermined cooking time, the fried foodis taken out and put on paper or an oil draining pan to remove excessoil. Now the frying operation is complete.

Therefore, with the conventional fryer the cooking oil remains at hightemperatures continuously even when no frying operation is performed.

The conventional fryer cannot easily collect deep-fried batter ballsthat disperse from food ingredients into the cooking oil during thefrying process, colloidal materials drifting away from the food beingfried, and impurities including water, smell and fat flowing out of thefood material. These unwanted materials that stay long in the cookingoil cause early degradation of the oil and darken its color, which inturn contaminate the food.

Further, since colloidal, floating oil dirt and deep-fried batter ballsadhere to food and sidewalls of the oil tank, the oil must be filteredinto a separate container every day to let floating substances to settleover time and the interior of the oil tank cleaned every day.

Generally, a range of temperature of the frying cooking oil agrees witha temperature range that accelerates early degradation and oxidation ofoil. In the conventional fryer, it is necessary to raise a largequantity of cooking oil to a set temperature in a short time and toprevent its temperature drop during the frying process and, if dropped,recover it to the set temperature in a short time. For this reason, theheater is operated at a temperature higher than the set temperature ofthe cooking oil. So, the oil in contact with the surface of the heaterin particular is subjected to a far higher temperature than the settemperature.

This accelerates degradation and oxidation of the cooking oil, increasesoil smoke and evaporation, and rapidly changes the composition of theoil. As a result, the conventional fryer needs to replace the cookingoil frequently, giving rise to a problem of a high economic burden.

In cooking, food materials are often covered with batters or breadcrumbs for frying. During frying, a large volume of batter and crumbscomes off the food, disperses into the cooking oil and is heated andcarbonized. This in turn darkens the oil and over time degrades itsquality. Therefore, to maintain the quality of the cooking oil,deep-fried batter balls and other discharged substances must be removedfrequently. However, this removal work is difficult considering theconvenience of the frying process and the construction of the fryer.

During the frying process, water in the food is replaced with thecooking oil. A large amount of water and water vapor flows out of thefood into the atmosphere and the cooking oil. The water discharged intothe atmosphere turns into smoke and, along with the oil, into oil mist,contaminating the interior of the kitchen and equipment. Further, thewater released into the cooking oil mixes with the oil over time,contributing to oxidation and degradation of the oil.

The water that did not mix with the cooking oil after being releasedinto the oil remains in a low-temperature oil layer between a lower partof the heater and the bottom of the oil tank. If the fryer is kept inoperation for a long period of time, the oil temperature in thelow-temperature oil layer increases and the water remaining at thebottom of the oil tank begins to evaporate, moving up from thelow-temperature oil layer to a high-temperature cooking oil layer. As itrises, the water is further heated and continues to expand its volumeuntil it is released into the atmosphere from an oil surface. If thisprocess is continued, there is a risk of the oil flowing over the oiltank.

For removing fine particles of the deep-fried batter balls and lipidsubstances, a means is available by which the cooking oils is drawn out,removed of the deep-fried batter balls floating in the oil as by filterpaper and then cleaned by a cleaner as the oil is returned to the tank.With this means, however, the water released into the oil cannot beremoved sufficiently. It is also difficult to perform the cleaning eachtime the fryer is used.

Patent document 1: Japanese Patent Disclosure No. 55-40249

Patent document 2: Japanese Patent Disclosure No. 60-9426

Patent document 3: Japanese Patent Disclosure No. 5-68440

The above-described conventional fryer keeps the cooking oil at anelevated temperature at all times even when not in use, in order to beready at any time to perform the frying operation. This deteriorates thecooking oil and shortens its life, leading to the frequent replacementof the oil. Furthermore, this mode of operation necessarily consumesheat energy wastefully for many hours.

Many, large and small deep-fried batter balls coming off the food aredispersed in oil layers and are difficult to remove completely with anexisting removal net. It is even more difficult to remove them duringthe frying process. In the case of a gas type fryer, a heater is fixedand the removal net cannot be inserted under the heater. So one possiblemethod may be to use a sucking type cleaner or another method mayinvolve drawing out the cooking oil from under the oil tank onto acontainer having the removal net therein and removing the unwantedsubstances. This, however, takes time and is practically impossible as ameans to be performed during the frying process. As a result, thedeep-fried batter balls are left in the cooking oil for many hours,shortening the life of the oil.

While the food is being fried, smoke, oil mist and water vapor arereleased from the oil surface in large quantities. Although the volumeof their release decreases when foods are not being fried, smoke and oilmist are always rising. A dedicated exhaust device installed above thefryer cannot discharge them sufficiently, leaving smell and possibleenvironmental contaminations.

Deep-fried batter balls coming off the food, colloidal substancesflowing out of it and floating in the oil, and water and smell releasedfrom the food material are spread widely into the entire oil duringcooking. In addition, there are lots of fine particles of these unwantedmaterials. Therefore they cannot be collected quickly, which in turnshortens the life of the oil, giving rise to an economic problem. Asdescribed above, leaving the unwanted deep-fried batter balls in the hotcooking oil for many hours causes smells, smoke and oil mist to adhereto equipment and human body, polluting the environment.

The present invention has been accomplished to overcome theabove-described problems and it is an object of this invention toprovide a fryer capable of preventing a degradation of cooking oil,securing a good kitchen environment and enhancing a work efficiency.

SUMMARY OF THE INVENTION

The fryer of this invention comprises: a water tank 32, 82 to storewater; an oil tank 9, 51 arranged above the water tank to store thecooking oil in contact with the stored water in the water tank; a heater13, 52 arranged in an oil layer in the oil tank; and an oil deliverypipe 10, 61 through which to draw the cooking oil in the oil layer by apump 29, 64 and release it onto a bottom of the water tank 32, 82;wherein the released cooking oil rises through the water layer and flowsinto a lower part of the oil layer.

Here, of the oil layers the oil layer formed above the heater 13, 52 isa high-temperature cooking oil layer and the oil layer formed below theheater 13, 52 is a low-temperature oil layer that has little degradationof oil.

The fryer according to this invention, as shown in FIG. 1, comprises: awater tank 32 to store water; an oil tank 9 installed above the watertank 32 to store cooking oil in contact with the stored water in thewater tank 32; a heater 13 arranged in an oil layer in the oil tank; apartition plate 15 arranged in a low-temperature oil layer below theheater 13 to receive impurities, such as deep-fried batter balls,falling down the cooking oil; and an oil delivery pipe 10 through whichto draw the cooking oil above the partition plate along with theseimpurities by a pump 29 and release it onto a bottom of the water tank32; wherein the released cooking oil rises through the water layer andflows into a lower part of the oil layer.

The fryer according to this invention has a pipe 25 installed betweenthe oil tank 9 and the water tank 32 and extending to evade thepartition plate 15 to communicate oil layers above and below thepartition plate 15.

The fryer according to this invention has a construction in which a heatexchange pipe 16 installed in an oil layer below the heater 13 iscommunicated with a heat accumulating unit 22 having its peripheryinsulated, and in which outer air or air heated by the heat accumulatingunit is sent between the heat exchange pipe and the heat accumulatingunit by a fan 23 to adjust the temperature of the cooking oil.

In this construction, the heat absorbed by the heat exchange pipe 16from the cooking oil in the oil layer is stored and maintained at anelevated temperature in the heat accumulating unit 22. When the fryingoperation is to be performed again, the heater 13, 52 is switched to ahigh temperature setting and the heat accumulated in the heataccumulating unit 22 is applied to the cooking oil, thereby recoveringthe cooking oil to a frying temperature in a short time.

Further, when the frying operation is not performed, a changeover switch(not shown) may be operated to switch the temperature setting of thecooking oil to a low temperature. At the same time, outer air isintroduced by the fan 23 into the heat exchange pipe 16 installed in theoil layer and then circulated to absorb the heat of the cooking oil,thereby lowering the temperature of the cooking oil layer to atemperature range where the oil is hardly oxidized or degraded.

The fryer according to this invention has an electrostatic dustcollecting plate 14 installed in the oil layer which adsorb finedeep-fried batter balls floating in the cooking oil.

The fryer according to this invention has a construction in which acover 2 put on a top of the oil tank 9 and opened and closed by a hinge5 has its interior communicated with a lower part of a water layer 20 ina cleaning tank 8; and in which a gas containing smoke, smell and oilmist produced from an oil surface is drawn by a suction fan 6 and passedthrough the water layer 20 to remove the gas of smell, smoke and oilbefore being exhausted to the atmosphere through a gas drain pipe 19.

The fryer according to this invention, as shown in FIG. 3 and FIG. 4,has a construction in which a filter water tank 71 having a filter 80 isinstalled close to the water tank 82; and in which impurities such asdeep-fried batter balls are drawn along with water into the filter watertank 71 from a water suction pipe inlet 74 at a bottom of the water tank82, with the impurities such as deep-fried batter balls left to settleon a bottom of the filter water tank and with water filtered by thefilter 80 returned to the water layer from a water supply opening 70provided in the water tank 82.

In this construction, the deep-fried batter balls, colloidal materialsdischarged from food, water and smell, all dispersed in the cooking oilduring the frying operation, are quickly drawn along with the cookingoil to a water layer in the lowest part of the oil tank and pushed intothe water. As a result, the oil is cleaned and cooled in the water as itrises through the water and then reaches the low-temperature oil layer.

The cooking oil therefore is kept at a low temperature at which the oilis hardly degraded. At the same time, the same volume of oil that hasbeen carried into the low-temperature oil layer moves up from thelow-temperature oil layer to the cooking oil layer above the oil heatingheater 52, where it is heated. So, the time during which the cooking oilremains hot can be shortened, preventing the degradation of oil andmaintaining the freshness and clarity of the oil.

The fryer according to this invention has a construction in which atemperature sensor 75 to detect a water temperature in the water tank 82is installed; and in which a water tank cooling fan 76 to lower thewater temperature in the water tank 82 is installed in a lower part ofthe water tank 82; wherein the temperature sensor and the water tankcooling fan are operated to adjust the water temperature in the watertank 82 and thereby adjust a temperature of the low-temperature oillayer below the heater 52.

The fryer according to this invention has a construction in which amixing prevention grid 62 made up of vertically arrayed plate pieces isinstalled near a boundary between a water layer and an oil layer aboveit to separate the water and oil layers and thereby prevent a mixing ofwater and cooking oil, which would otherwise be caused by the release ofthe cooking oil from the oil delivery pipe 61 at the bottom of the watertank 82 and by the release of water from the water supply inlet 70 ofthe filter water tank 71.

The fryer according to this invention has a construction in which adispersion plate 68 to scatter around the cooking oil rising through thewater layer is installed in a path in which the cooking oil releasedfrom the bottom of the water tank 82 rises, so that the cooking oil willnot directly rise to the hot cooking oil layer.

The fryer according to this invention has a construction in which, inaddition to the heater 52 that operates at an elevated temperature, anauxiliary heater 81 for adjusting a temperature of the heater isconnected in series with the heater to work as a low-temperature heater;and in which wherein a cylindrical inner case 78 for preventingcontamination of an inner sidewall surface of the oil tank 51 isprovided inside the oil tank to cover the inner sidewall surface of theoil tank.

Since the fryer of this invention has a construction in which the oiltank is arranged above the water tank, in which the heater is installedin the oil layer of the oil tank, and in which the cooking oil in theoil layer is drawn by the pump and released onto the bottom of the watertank through the oil delivery pipe, so that the released cooking oilrises through the water layer and flows into a lower part of the oillayer. This construction allows deep-fried batter balls and dischargedmaterials from food, all produced during the frying process, to beforcibly cleaned with water along with the cooking oil. Thisconstruction can also secure a low-temperature oil layer. As a result,the degradation of cooking oil can be minimized, reducing the frequencyof replacing the cooking oil with new oil, which is economical. Further,the work environment can be protected against contamination, assuring agood cooking environment.

Moreover, in addition to the main heater that operates at an elevatedtemperature, an auxiliary heater is connected in series with the mainheater to adjust the temperature of the main heater. This also producesthe effect described above.

In addition to the advantages and effects described above, the fryer ofthis invention, which has the partition plate arranged in thelow-temperature oil layer, also offers an advantage of being able toefficiently collect impurities such as deep-fried batter balls fallingdown the cooking oil.

The fryer of this invention employs the construction in which air heatedby the heat accumulation unit communicating with the heat exchange pipeis introduced or discharged by the fan to adjust the temperature of thecooking oil. This construction allows the temperature of the cooking oilto go down to a low temperature in a short time, preventing degradationof the oil that is standing by for cooking. Further, by applying theheat accumulated in the heat accumulation unit to the cooking oil, thecooking oil can be returned to a high cooking temperature in a shorttime, facilitating the work and putting the heat to an effective use.

With the fryer of this invention, since the electrostatic dustcollecting plate is installed in the oil layer, super-fine solidparticles are adsorbed by the electrostatic dust collecting plate. Thecooking oil cleared of impurities is recirculated into the cooking oillayer. Thus the degradation of cooking oil can be minimized, reducingthe frequency of oil replacement, which is economical.

With the fryer of this invention, since the interior of the cover of theoil tank is communicated with the cleaning tank and smoke produced fromthe oil surface is drawn by the fan and passed through the water layer,the air can be efficiently removed of smoke, smell and oil mist,improving the work environment.

With the fryer of this invention, since the water cooled by the coolingfan installed at the bottom of the water tank is drawn along withimpurities such as deep-fried batter balls into the filter water tank,from which the filtered water is returned to the water tank, the timeduring which the cooking oil is kept at an elevated temperature isshortened, minimizing the degradation of oil, maintaining the clarityand freshness of the cooking oil. There is also an advantage that thewater can be filtered in the filter water tank along with theimpurities.

With the fryer of this invention, since the mixing prevention grid isinstalled near a boundary between the water layer and the oil layer, themixing of water and cooking oil, which would otherwise be caused by therising cooking oil released from the bottom of the water tank or by therelease of water, can be prevented.

With the fryer of this invention, since the dispersion plate to scatteraround the cooking oil rising through the water layer is installed in apath in which the cooking oil released from the bottom of the water tankrises, the cooking oil that has passed through the water layer can beprevented from quickly rising through the low-temperature oil layer tothe cooking oil layer. This offers an advantage of being able tomaintain a good cooking environment for the oil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a fryer according to a firstembodiment of this invention.

FIG. 2 is a schematic plan view of the fryer according to the firstembodiment.

FIG. 3 is a schematic side view of a fryer according to a secondembodiment of this invention.

FIG. 4 is a schematic plan view of the fryer according to the secondembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, preferred embodiments of the present invention will be described.

FIG. 1 and FIG. 2 illustrate a fryer according to a first embodiment ofthis invention. FIG. 1 is an explanatory side view of the fryer. Denoted9 is an oil tank 9, 32 a water tank 32, and 13 an electric heater 13 toheat cooking oil in the oil tank. In the oil tank 9 there are formed ahigh-temperature cooking oil layer (I) above the heater 13 and alow-temperature oil layer (II) below the heater 13. Below thelow-temperature oil layer (II) is installed a partition plate 15. Belowthe oil tank 9 is provided the water tank 32. Between a water layer (IV)in this water tank 32 and the partition plate 15 there is formed an oilstorage layer (III) to store oil.

A temperature sensor (not shown) is installed in the frying oil layer(I) to maintain the oil temperature. When the oil temperature fallsbelow a set level, the heater 13 is turned on to start heating to keepthe oil at the set temperature.

The oil tank 9 is separated by the partition plate 15 arranged slightlytilted in the oil layer below the heater 13. The partition plate 15receives impurities such as deep-fried batter balls falling down thecooking oil.

The water tank 32 and the oil tank 9 are connected by a pipe 25 havingan oil inlet 27 and an oil outlet 26 in a manner that avoids thepartition plate 15.

Close to the upper surface of the partition plate 15 there is providedan oil outlet 28, through which the cooking oil including deep-friedbatter balls near the upper surface of the partition plate 15 is drawnout by an oil delivery pump 29 driven by a screw pump drive motor 4installed in an oil delivery pipe 10. The cooking oil thus drawn outfrom the oil outlet 28 is released through a three-way valve 35 at thelower end of the oil delivery pipe 10 and through an oil supply anddischarge pipe 34 out into the bottom of the water tank 32.

The cooking oil released onto the bottom of the water tank 32 floats upthe water layer (IV), by its own specific gravity difference, into theoil storage layer (III). At the same time, the water and deep-friedbatter balls fall onto the bottom of the water layer (IV), pushing thecooking oil in the oil storage layer (III) to move from the oil inlet 27and the oil outlet 26 into the cooking oil layer (I).

A heat exchange pipe 16 and a heat accumulating unit 22 constitute aheat accumulate and release device, which is shown in FIG. 2, a planview.

When the cooking oil temperature falls down to a specified value belowthe set temperature, as when a large volume of food material is throwninto the fryer and the oil temperature cannot rise only by the heatproduced by the heater 13, a fan 23 is operated to circulate heataccumulated in the heat accumulating unit 22 through the heat exchangepipe 16 in the form of hot air to help raise the temperature of thecooking oil in a short time.

If the next frying operation is not performed immediately following theprevious one, the oil temperature needs to be lowered as quickly aspossible to keep the composition of the oil intact.

For that purpose, the present invention provides a changeover switch(not shown) which is switched to a standby side after the fryingoperation to form a low-temperature setting circuit to shut off thefrying temperature setting circuit, allowing the cooking oil to go downslowly. At the same time, an external air introducing fan 37 for theheat accumulating unit 22 is energized to open a trap door 39, sendingthe outer air into the heat exchange pipe 16.

The air delivered into the heat exchange pipe 16 is heated by the heataccumulated there by the cooking oil and is carried into the heataccumulating unit 22, from which the heated air is exhausted from a trapdoor 40, thus realizing a reduction in the oil temperature. The heattaken from the cooking oil is accumulated and stored in the heataccumulating unit 22 enclosed by an insulation layer 21. If necessary,the heat accumulating unit 22 is maintained at a set temperature by adedicated internal heater (not shown).

When one wants to perform a frying operation, he or she switches thechangeover switch from the standby side to the cooking side to put theheater 13 at the high-temperature setting. At the same time, the fan 23is turned on to deliver the hot air from the heat accumulating unit 22into the heat exchange pipe 16 to raise the cooking oil to the settemperature in a short time.

Suppose, for example, the heater consumes 3 kW using a three-phase 200 Vas a power supply, that the high-temperature cooking oil layer (I) has avolume of 3 liters, and that the sheathed heater has a heat efficiencyof 80%. Then, for the cooking oil layer to be heated from the low settemperature of 140° C. to about 170° C. in three minutes and then toreach the initial set temperature of 180° C., it takes four minutes ifonly the heater is used. At the same time, by adding the heat of theheat accumulating unit 22 to the cooking oil through the heat exchangepipe 16, the initial set temperature can be recovered in two minutes anda half, thus shortening the waiting time.

The amount of deep-fried batter balls deposited at the bottom of thewater tank 32 can be checked from a peep window 31 of the water tank.Turning the three-way valve 35 to a discharge side allows the deep-friedbatter balls and discharged materials and the water in the water layerto flow down a discharge pipe 36 into drainage through a deep-friedbatter ball collector.

Along with the discharged water the cooking oil also flows down. When awater level float 17 lowers, a valve of a water supply nozzle 33 opens,automatically supplying water from the water supply nozzle 33 directlyconnected to a city water into the water tank 32. After confirmingthrough the peep window 31 that the interior of the water tank iscleaned, an operator closes the three-way valve 35 to stop thedischarge. The water from the water supply nozzle 33 automatically stopswhen the water level float 17 reaches the water level.

In replacing the cooking oil in the oil tank 9, an oil drain valve 30 isopened to allow the entire oil in the high-temperature cooking oil layer(I), the low-temperature oil layer (II) and the oil storage layer (III)to flow into a container. Since the oil drain valve 30 is located abovethe water level, the water in the water layer (IV) does not flow outalong with the oil.

In FIG. 1, a box-shaped cover 2 is supported on the oil tank 9 by acover hinge 5. Air intake openings 3 are arranged in the entire innersurface of the cover 2. As an air intake fan 6 rotates, smoke, watervapor and oil mist from oil surface are sucked out from the air intakeopenings 3 and led to the bottom of a water layer 20 of a cleaning tank8, in which they are cleaned as they rise through the water layer 20 andexhausted from a gas release pipe 19. This operation is performed onlywhen the temperature setting circuit is in operation, in order to suckand clean the smoke, water vapor and oil mist produced during the fryingprocess. This operation is not stopped even when the cover is opened.

As described above, the fryer of this embodiment has a heating deviceand a heat dissipating device. The heating device comprises the heataccumulating unit and the heat exchange pipe and is capable of raisingthe cooking oil temperature in a short time to assist the heater. Theheat dissipating device introduces an open air directly into the heatexchange pipe to cool the oil in a short time. These two devices combineto limit heat losses during the standby and thereby prevent degradationof the oil.

Further, the fryer of this embodiment has a deodorizing, smokeelimination device that cleans smoke, smell, oil mist and water vaporwith water before releasing them into the atmosphere. Therefore, duringthe frying operation, deep-fried batter balls and other dischargedmaterials are automatically collected at all times and the simpleexhaust device eliminates the possibility of smoke, smell and oil mistfloating around.

FIG. 3 and FIG. 4 illustrate a fryer according to a second embodiment ofthis invention. In these figures, elements identical with those of thefirst embodiment are given like reference numerals.

FIG. 3 is an explanatory side view of the fryer. Denoted 51 is an oiltank, 82 a water tank, and 52 an electric heater to heat the cooking oilin the oil tank. In the oil tank 51 there are a high-temperature cookingoil layer (I) above the heater 52 and a low-temperature oil layer (II)below the heater 52. In the water tank 82 provided below the oil tank51, a water layer (IV) is formed.

Denoted 64 is a screw-type pump that draws the high-temperature oilalong with deep-fried batter balls floating in the oil into an oiltransfer pipe 61 from an oil transfer pipe inlet 56 and delivers it froman oil supply opening 73 into the water layer (IV). The oil is separatedfrom the deep-fried batter balls as they rise through the water. The oilis cleaned efficiently in this manner.

If the pump 64 that draws the high-temperature cooking oil layer (I) isoperated at high speed, the oil and the water in the oil are mixed,clouding the oil white and degrading the oil quality. It is thereforedesirable to operate the pump 64 at a low speed of 400 rpm and to havethe screws of the pump arranged at a low pitch.

Designated 79 is a drain valve 79 for draining water and oil and is usedto replace the water layer (IV) and the cooking oil. When adding waterto maintain the water level after the draining, the water may be pouredinto the cooking oil layer (I) from the oil surface. For correct waterlevel, it is desirable to have a water level meter.

The drain valve 79 is also used to discard the cooking oil layer (I) andthe low-temperature oil layer (II).

A suction pump 67 installed in a water suction pipe 77 opening to thewater tank 82 is operated during the frying process and at predeterminedtimes to collect deep-fried batter balls deposited at the bottom of thewater layer (IV) and to keep the water layer at a low temperature.

With the suction pump 67 in operation, the water and crumbs carried intoa filter water tank 71 are mixed with water already stored there to fillthe water tank. Since the cover of the filter water tank is hermeticallyclosed, the pressure within the tank increases causing the waterfiltered by a filter 80 to be returned to the water layer (IV) from adischarge pipe inlet 59 and a water supply inlet 70.

As described above, this process of drawing water from a water suctionpipe inlet 74 and returning it to the filter water tank 71 is repeatedto clear the bottom of the water layer and collect the deep-fried batterballs.

In this fryer, the low-temperature oil layer (II) is intended to storethe oil of the high-temperature cooking oil layer (I) after having beencleaned at a low temperature for a while. Although the low-temperatureoil layer (II) is cooled by the water of the water layer (IV), the upperpart of the low-temperature oil layer (II) is connected to thehigh-temperature cooking oil layer (I) and thus susceptible to anelevated temperature.

Therefore, to keep the temperature of the water layer (IV) constant andminimize an increase in the temperature of the low-temperature oil layer(II), the suction pump 67 is started when a water temperature rises to aset temperature, delivering the water of the water layer to the filterwater tank 71 where the water is filtered and mixed with the cooledwater before being returned to the water layer. Since the fluiddelivered by the pump is water and its temperature is low at 50° C. andsince the head of the pump is small, an existing small water pump can beused.

Further, a water tank cooling fan 76 installed at the bottom of thewater tank 82 to minimize an increase in temperature of the water in thewater tank 82 may be small in size.

The water in the water tank 82 and the water in the filter water tank 71are replaced during the frying process and according to a predeterminedprogram. When the water in the water tank 82 is supplied to the filterwater tank 71, the water rotates in vortex about the water suction pipeinlet 74 as a center. So, there is a possibility of the water in anupper part of the water layer in contact with the low-temperature oillayer (II) getting mixed with oil.

Further, the release of the cooking oil from the oil delivery pipe atthe bottom of the water tank or the release of water from the filterwater tank can cause the water and the cooking oil to be disturbed andmixed.

To forestall these possibilities, a mixing prevention grid 62 made up ofvertically arranged plate pieces for separating water and oil isinstalled at a boundary between the water layer and the low-temperatureoil layer.

The oil drawn from the cooking oil layer (I) is released into the waterlayer (IV) and cooled as it rises to the low-temperature oil layer (II).At this time, since its temperature is higher than that of thelow-temperature oil layer, the oil may rise quickly to the cooking oillayer. To prevent this, a dispersion plate 68 for temporarily holding alump of the cooking oil rising through the water layer and scattering itaround is installed directly above the oil supply opening 73, i.e., in apath in which the oil is rising, thereby causing the oil to rise slowlyup to the low-temperature oil layer as it is cooled by the water of thewater layer.

Considering the fact that the water temperature is below 50° C. and forthe purpose of checking the rising oil from above the cooking oil layer,the dispersion plate 68 is preferably made of a transparentpolycarbonate.

In addition to the main heater 52 that operates at an elevatedtemperature, an auxiliary heater 81 is also provided for adjusting theheater temperature. Both of these heaters can be connected in series asrequired to work as a low-temperature heater.

That is, when raising the oil temperature at an initial stage, thelow-temperature heater using the series-connected circuit is activated.This low-temperature heater is operated also to keep the oil at the settemperature to prevent oil degradation.

When a sensor detects a temperature drop of 5° C., as when a frozen foodmaterial is thrown in, the high-temperature main heater 52, excludingthe series-connected auxiliary heater 81, is activated to rapidlyrecover the oil temperature to the cooking temperature.

In the oil tank 51 an inner case 78 extending from the upper end of theoil tank down to the lower part of the cooling oil layer (I) isremovably installed to cover and prevent the inner sidewall surface ofthe oil tank 51 from being contaminated.

This inner case 78 can normally protect the inner sidewall surface ofthe oil tank 51 from being contaminated with oil dirt. It can also betaken out and cleaned, as required, without drawing oil from the tank.This is proven to have the same effect as when the sidewall surface ofthe oil tank 51 is cleaned in an ordinary way. The inner case 78 needonly be formed of a stainless steel plate with a handle.

With the above embodiment, the life of the cooking oil and the period inwhich the oil remains clean can be prolonged, enhancing economy. At thesame time, deep-fried batter balls and materials discharged from thefood are automatically drawn and collected by a pump, facilitating thecleaning of the oil. This process allows even fine particles of crumbs,which could not have been collected by the conventional net, to bequickly removed, making the cleaning easy. Except during the cooking,the oil is rested at a low temperature, contributing to a longer life ofoil. This in turn allows the use this fryer in such applications where along hour, continuous operation is essential or in such stores thatremain open for many hours. This fryer can be realized in a low-costconstruction.

When the frying operation is finished, the suction pump 67 is activatedfor a predetermined time to continuously draw from the water suctionpipe inlet 74 into the filter water tank 71 the deep-fried batter ballsthat have fallen from the cooking oil layer and are lying on the bottomof the water tank 82 and crumbs and colloidal materials discharged fromthe food and floating in the water of the water tank 82 after the oilcleaning. So, the interior of the water tank 82 is kept clean at alltimes.

The conventional deep-fried batter ball collecting net becomes obviated.As for the cleaning operation performed after the business hours, thereis no need to draw oil from the tank and filter it. The only processrequired includes removing the contamination prevention inner case 78and cleaning it of adhering dirt, thus shortening the time it takes toclean the oil tank. Further, the two oil heaters can be used: one is ahigh-temperature main heater to deal with a sudden drop of oiltemperature during the frying operation; and the other is an auxiliaryheater connected in series with the main heater to work as alow-temperature heater during the normal operation. These two heatersare automatically switched to keep the oil temperature constant aspractically as possible. The fryer of this construction can prolong thelife of the oil.

1. A fryer comprising: a water tank to store water; an oil tankinstalled above the water tank to store cooking oil in contact with thestored water in the water tank; a heater arranged in an oil layer in theoil tank; and a filter water tank having a filter and installed close tothe water tank; wherein impurities such as deep-fried batter balls aredrawn along with water into the filter water tank from a water suctionpipe inlet at a bottom of the water tank, with the impurities such asdeep-fried batter balls left to settle on a bottom of the filter watertank and with water filtered by the filter returned to the water layerfrom a water supply opening provided in the water tank
 2. A fryeraccording to claim 1, wherein a heat exchange pipe installed in an oillayer below the heater communicates with a heat accumulating unit havingits periphery insulated; and wherein outer air or air heated by the heataccumulating unit is sent between the heat exchange pipe and the heataccumulating unit by a fan to adjust the temperature of the cooking oil.3. A fryer according to claim 1, wherein an electrostatic dustcollecting plate to absorb fine deep-fried batter balls floating in thecooking oil is installed in the oil layer.
 4. A fryer according to claim1, wherein a cover put on a top of the oil tank and opened and closed bya hinge has its interior communicating with a lower part of a waterlayer in a cleaning tank; and wherein a gas containing smoke, smell andoil mist produced from an oil surface is drawn by a suction fan andpassed through the water layer to remove the smell, smoke and oil mistof gas before being exhausted to the atmosphere through a gas drainpipe.
 5. A fryer according to claim 1, wherein a temperature sensor todetect a water temperature in the water tank is installed; wherein awater tank cooling fan to lower the water temperature in the water tankis installed in a lower part of the water tank; and wherein thetemperature sensor and the water tank cooling fan are operated to adjustthe water temperature in the water tank, and thereby adjust thetemperature of the low-temperature oil layer below the heater.